Method of separating a medium into a solids-containing component and a liquid component

ABSTRACT

A medium is separated into a solids-containing component and a liquid component. The latter flows through a filter. Clogging of the filter is avoided in that the latter is moved relative to the medium perpendicularly to the flow direction of the liquid through the filter element. At the same time, the medium is agitated.

CROSS-REFERENCE TO RELATED APPLICATION

This is a division of U.S. application Ser. No. 08/976,731, filed Nov.24, 1997, now U.S. Pat. No. 5,928,508 which was a continuation ofinternational application No. PCT/DE96/00803, filed May 9, 1996.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to a method for separating a medium into asolids-containing component and a liquid component, particularly for thedewatering and drying of waste sludge from nuclear plants, in which theliquid component flows through a filter. The invention relates,furthermore, to an apparatus for carrying out the method.

Various types of solids-containing radioactive waste sludge are producedin nuclear power plants, such as, for example, spheroidal or pulverulentresin sludge or lapping agent suspensions. In order to ensureappropriate intermediate or final storage, waste sludge of this typemust first be dewatered and dried before further treatment, for example,before being bound in bitumen or pressed under high pressure.

As a result of the dewatering which precedes drying and in whichcapillary and/or gusset water is separated off and fed to a waste watersystem, a high material throughput with low energy consumption andtherefore effective treatment of the waste can be achieved.

Suction filters are normally used in the dewatering operations of thistype. The medium to be dewatered is thereby subjected to excess pressurein a vessel, in the bottom region of which a filter element is arranged.The liquid component of the medium, for example the gusset water, isthereby forced through the filter element. The solids-containingcomponent of the medium is retained by the filter element. Thesolids-containing filter residue is then normally supplied to a dryingstage.

However, the filter elements of such suction filters become cloggedrather quickly and they require cleaning or exchange after only shortoperating periods.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide a method anddevice for separating a medium into a solids-containing component and aliquid component, which overcomes the above-mentioned disadvantages ofthe heretofore-known devices and methods of this general type and whichprevents clogging of the filter even at a low outlay in terms ofcleaning or maintenance.

With the foregoing and other objects in view there is provided, inaccordance with the invention, a method of separating a medium into asolids-containing component and a liquid component. The method comprisesthe following steps:

agitating a medium containing solids and liquid;

conducting the liquid through a filter in a given throughflow direction;and

simultaneously moving the filter relative to the medium substantiallyperpendicularly to the given throughflow direction for stripping offfilter residue.

In accordance with an added feature of the invention, the agitating stepcomprises agitating waste sludge of a nuclear power plant and the filterresidue is further dewatered and dried.

In other words, the objects of the invention are satisfied in that thefilter, for the purpose of stripping off filter residue, is movedrelative to the medium in a direction substantially perpendicular to thethroughflow direction, and in that the medium is stirred or agitated.

The invention is based on the premise that, when a filter becomesclogged, first some solid particles contained in the medium adhere tothe filter. These then lump together with further solid particles intheir vicinity. This may continue until the filter is cloggedcompletely. Clogging of the filter may therefore be avoided or impededby suppressing the adhesion of solid particles to the filter. In orderto suppress the adhesion of solid particles to the filter, a relativemovement between the filter and the medium to be separated which takesplace approximately perpendicularly to the throughflow direction hasproved particularly effective.

In order further to assist the separation of liquid andsolids-containing components of the medium, the latter is additionallyagitated. Moreover, this is conducive to the transport of heat withinthe medium, so that the medium is heated more easily and the dewateringis assisted or the drying operation is accelerated.

In order to make it easier to treat a radioactive medium in a particularway, after a first dewatering or drying step the medium may be scavengedby supplying non-radioactive water before it undergoes a seconddewatering or drying step.

With the above and other objects in view, there is further provided, inaccordance with the invention, an apparatus for separating a medium intoa solids-containing component and a liquid component, comprising:

a vessel for receiving a medium containing solids and liquid, the vesselhaving a wall with an inner wall surface;

a cylindrical filter element rotatably mounted in the vessel;

an intermixing member and a rotatable pivoting arm carrying theintermixing member disposed within the vessel such that the intermixingmember is guided along the inner wall surface when the pivoting armrotates.

In other words the objects set for the apparatus are satisfied with acylindrical filter element that rotates in the vessel, and in that thereis arranged on a rotatable pivoting arm provided within the vessel anintermixing member which can be guided along the inner surface of thevessel when the pivoting arm rotates.

During a dewatering and drying operation, the filter element rotatesabout its cylinder axis, so that a movement of the filter elementrelative to the medium in a direction approximately perpendicular to thethroughflow direction is achieved. The adhesion of solid particlescontained in the medium to the filter element is thereby suppressed, sothat clogging of the filter element is virtually ruled out.

Circulation and therefore intermixing of the medium is possible by meansof the intermixing member, so that the separation of the medium into asolids-containing and a liquid component and also the transport of heatwithin the medium are assisted. Moreover, by guiding the intermixingmember along the inner surface of the vessel, the adhesion of solidparticles contained in the medium to the vessel wall is avoided. Suchadhesion, particularly in the case of a radioactive medium, could leadto additional contamination of the vessel.

In order to make it possible to heat the medium located in the vessel,the vessel advantageously has a double-walled design, a hot steam feedconduit being connected to the vessel double wall. Furthermore, a feedconduit and/or a discharge conduit for compressed air may be arranged onthe vessel.

In a further advantageous design, the filter element has a metal screen.Metal screen filters of this type have proved particularly effective forthe dewatering of radioactive waste sludge.

In order to ensure that the separated liquid component of the medium isdischarged even when the vessel has small filling quantities, a filtrateoutflow pipe reaches virtually to the bottom of the filter element. Thepipe thereby is disposed within the filter element. Moreover, anyinfiltrations of air into the filtrate discharge conduit when the vesselis subjected to excess pressure are avoided by means of the filtrateoutflow pipe.

The advantages achieved by means of the invention are, in particular,that clogging of the filter is avoided, even at a low outlay in terms ofcleaning or maintenance, by means of a movement of the filter relativeto the medium perpendicularly to the throughflow direction during theseparation of a medium into the solids-containing component and theliquid component. This is particularly advantageous during thedewatering and drying of waste sludge from nuclear plants during whichthe liquid component flows through a filter.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin a method and apparatus for separating a medium into asolids-containing component and a liquid component, it is neverthelessnot intended to be limited to the details shown, since variousmodifications and structural changes may be made therein withoutdeparting from the spirit of the invention and within the scope andrange of equivalents of the claims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWING

The sole FIGURE is a diagrammatic view of a system according to theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the sole figure of the drawing in detail, there isshown an apparatus 1 for separating a medium into a solids-containingcomponent and a liquid component. The separating apparatus 1 comprises avessel 2 which is conical in a region 3 and which has a double-walledstructure. The conicity of the vessel 2 renders it conducive to completeemptying of the vessel 2 through a narrowed drainage orifice 4. Thedrain 4 can be closed by means of a cover or a valve. A pivoting arm 6is disposed within the vessel 2 which is rotatable about a center axisof the cone and at the end of which there is disposed an agitator 8. Theagitator 8, which is itself rotatable, is an intermixing member. Theagitator 8 is disposed such that it brushes along the conical innersurface 10 of the vessel 2 when the pivoting arm 6 rotates.

A cylindrical filter element 12 is arranged within the vessel 2coaxially with the cone axis so as to be rotatable about its cylinderaxis. In the preferred embodiment, the filter element 12 is formed froma metal screen. A filtrate outflow pipe 14 is arranged in the cylinderaxis of the filter element 12. The pipe 14 is connected to a filtratedischarge conduit 16 outside the vessel 2. The filtrate outflow pipe 14reaches virtually as far as the bottom of the filter element 12.

A compressed air feed conduit 18, which can be shut off by means of avalve, a water feed conduit 19, and a material feed conduit 20communicate with the vessel 2. In order to make it possible to scavengeand/or blow out the filter element 12, the compressed air conduit 18 isconnected to the filtrate discharge conduit 16 via a conduit 22. A valve21 is provided for selectively shutting off the connection between thepipe 16 and the air conduit 18.

A stationary or movable vessel 24 is provided underneath the drainageorifice 4 of the vessel 2. The drainage can be closed with a valve 23.In order to assist a filtering operation, both the valve 23 and thelower part of the conical region 3 may be designed as filters. A hotsteam feed conduit 26 and a discharge conduit 28 are connected to thedouble-walled conical region 3 of the vessel 2.

In operation, the vessel 2 is filled to a level 30 with a medium M, forexample waste sludge from a nuclear plant. The waste sludge is fed inthrough the feed conduit 20 and is to be separated into a liquidcomponent and a solids-containing component. To separate the liquidcomponent from the solid component of the medium M, the vessel 2 issubjected to excess pressure by means of the compressed air feed conduit18. The liquid component of the medium M is thereby forced through thefilter 12 and it reaches the interior of the filter element 12 in theform of a filtrate F. Due to the pressure ratios, the filtrate F exitsvia the filtrate outflow pipe 14 to the filtrate discharge conduit 16and via the latter to a non-illustrated separating vessel. Thesolids-containing component of the medium M is thus enriched in thevessel 2, so that the medium M is dewatered. For this purpose, thefiltrate outflow pipe 14 reaches virtually as far as the bottom of thefilter element 12, so that the infiltration of air from the vessel 2subjected to excess pressure into the filtrate discharge conduit isavoided even in the case of a low level 30. In order to avoid cloggingthe filter element 12 with solid particles contained in the medium M,the filter element 12 rotates about its cylinder axis. In other words:the filter element 12 is thus moved relative to the medium Mperpendicularly to the throughflow direction.

Hot steam is fed to the double-walled conical region of the vessel 2 viathe hot steam feed conduit 26. As a result, the medium M is heated.Heating the medium M in this way assists in the separation of the liquidcomponent from the medium M and therefore the dewatering and also dryingof the solids-containing component of the medium M. The pivoting arm 6rotates jointly with the filter element 12. The similarly rotatingagitator 8 is disposed on the pivoting arm. The continuous intermixingof the medium M in the vessel 2 which is thus achieved is conducive toseparating the medium M into a solids-containing component and a liquidcomponent. Moreover, the transport of heat within the medium M isthereby assisted, so that it becomes easier to heat the medium M.Furthermore, the agitator 8 guided along the inner wall 10 of the vessel2 prevents the adhesion of solid particles of the medium M to the vesselinner wall 10 and therefore contamination of the vessel 2 in the case ofthe treatment of radioactive materials.

After the solids-containing component of the medium M has been dewateredand dried, the remaining residue R is fed to the vessel 24 by openingthe drainage valve 22. The interior of the filter element 12 mayadditionally be put under excess pressure by means of the compressed airfeed conduit connected to the filter discharge conduit 16, so that itbecomes possible for the filter element 12 to be blown out in reverse.

In the case of the treatment of a radioactive medium M, after a firstdewatering step the latter may initially be scavenged by feeding water Wthrough the water feed conduit 19. This results in a diluting effect.

The separating apparatus 1 affords the additional advantage of a compactconstruction and makes it possible to carry out the various treatmentprocesses, such as dewatering, scavenging or drying, within a singlevessel 2. This is advantageous particularly in the case of the treatmentof radioactive waste sludge. The rotation of the filter element 12 andof the agitator 8 on the rotating pivoting arm 6 ensures an effectiveseparating operation, while the clogging of the filter element 12 isavoided, even at a low outlay in terms of cleaning or maintenance.

We claim:
 1. A method of separating a medium into a solids-containingcomponent and a liquid component, which comprises:providing a vesselhaving an inner wall surface; intermixing a medium containing solids andliquid by guiding an intermixing member along the inner wall surface ofthe vessel; conducting the liquid through a filter of a filter element,in a given throughflow direction, the filter element having a bottom;conducting the liquid virtually from the bottom upwardly within thefilter element; and simultaneously moving the filter relative to themedium substantially perpendicularly to the given throughflow directionfor stripping off filter residue.
 2. The method according to claim 1,wherein the intermixing step comprises intermixing waste sludge of anuclear power plant and the filter residue is dewatered and dried. 3.The method according to claim 1, which further comprises heating themedium.
 4. The method according to claim 1, which comprises recoveringthe medium after a first dewatering or drying step.
 5. The methodaccording to claim 1, which further comprises heating the inner wallsurface of the vessel.